A transmitter optical subassembly (TOSA) that converts an electrical signal into an optical signal and a receiver optical subassembly (ROSA) that converts an optical signal into an electrical signal are used in optical interconnections that, using optical fibers, transmit data in parallel between chips, boards, or racks (see, e.g., Japanese Patent Application Laid-Open Publication Nos. 2005-338408, H11-345955, H9-197158, H7-209558, and H5-134137).
FIG. 26 is a perspective diagram of an optical interconnecting module. As depicted in FIG. 26, an optical interconnecting module 2610 is a module that connects multiple boards 2620 through optical fibers 2630. The optical interconnecting module 2610 includes an optical transmitting module 2640 and an optical receiving module 2650.
The optical transmitting module 2640 includes a transmitting circuit 2641 and an optical subassembly 2642. The transmitting circuit 2641 outputs to the optical subassembly 2642, an electrical signal that is based on a data signal transmitted from a circuit element of the board 2620. The optical subassembly 2642 includes a laser diode (LD) and is a TOSA that emits through an optical fiber 2630, an optical signal that is based on the electrical signal output from the transmitting circuit 2641.
The optical receiving module 2650 includes an optical subassembly 2651 and a receiving circuit 2652. The optical subassembly 2651 includes a photo detector (PD) and is a ROSA that outputs to the receiving circuit 2652, an electrical signal that is based on the optical signal received through the optical fiber 2630. The receiving circuit 2652 demodulates, into a data signal, the electrical signal output from the optical subassembly 2651 and outputs the demodulated data signal to a circuit element of a board 2620.
FIG. 27 is a front cross-sectional view of a conventional optical subassembly. As depicted in FIG. 27, the conventional optical subassembly 2700 includes a optoelectronic converting element 2720 such as an LD disposed on a wiring substrate 2710, and a metal cap 2730 that hermetically seals the optoelectronic converting element 2720. The wiring substrate 2710 is provided with a lead pin that connects the optoelectronic converting element thereto, etc. The metal cap 2730 is provided with a lens member 2740.
When the optoelectronic converting element 2720 is an LD, the optical subassembly 2700 emits an optical signal generated by the LD, through the lens member 2740. When the optoelectronic converting element 2720 is a PD, the optical subassembly 2700 receives an optical signal entering through the lens member 2740. The metal cap 2730 is fitted with a ferrule, etc., to connect an optical fiber thereto.
FIG. 28 is a front cross-sectional view of alignment of the optical axes of the conventional optical subassembly. In FIG. 28, a reference numeral “2721” denotes the optical axis of the optoelectronic converting element 2720. A reference numeral “2741” denotes the optical axis of the lens member 2740. In the conventional optical subassembly 2700, to improve its optical property, the lens member 2740 is positioned relative to the optoelectronic converting element 2720 that is disposed on the wiring substrate 2710 such that the optical axis 2721 and the optical axis 2741 coincide with each other.
When the optoelectronic converting element 2720 is an LD, an optical signal that is emitted from the LD and that passes though the lens member 2740 is monitored and the lens member 2740 is positioned such that the intensity of the optical signal monitored becomes maximal. When the optoelectronic converting element 2720 is a PD, an electrical signal output from the PD based on an optical signal entering through the lens member 2740 is monitored and the lens member 2740 is positioned such that the intensity of the monitored electrical signal becomes maximal.
When the lens member 2740 is positioned, the metal cap 2730 is fixed on the wiring substrate 2710 by a method such as soldering. Thereby, the optoelectronic converting element 2720 is hermetically sealed by the wiring substrate 2710 and the metal cap 2730. A space having the optoelectronic converting element 2720 hermetically sealed therein has a shape of, for example, a cylinder having the diameter of 5 to 6 mm and the height of 5 to 6 mm.
When the optoelectronic converting element 2720 is positioned on the wiring substrate 2710, self-alignment is used where electrodes of the optoelectronic converting element 2720 are disposed on solder bumps disposed on the wiring substrate 2710; the solder bumps are heated and melted; and thereby, the optoelectronic converting element 2720 is positioned on the wiring substrate 2710 in a self-aligning manner due to the surface tension of the melted solder bumps.
However, in the above conventional technique, the metal cap 2730 to hermetically seal the optoelectronic converting element 2720 is necessary and, therefore, a problem arises in that the optical subassembly 2700 becomes large (for example, the diameter is 5 mm and the height is 5 mm) because a coupling portion is present between the lens member 2740 and the metal cap 2730. Therefore, another problem arises in that, for example, the mounting density demanded in the optical interconnection (for example, arrangement at intervals of 0.25 mm) is unable to be satisfied.
Because the lens member 2740 is positioned by monitoring the output signal of the optoelectronic converting element 2720, another problem arises in that the positioning of the lens member 2740 takes time and, therefore, the manufacture of the optical subassembly 2700 also takes time. Because a monitoring apparatus that monitors the output signal of the optoelectronic converting element 2720 and a positioning apparatus that positions the lens member 2740 are necessary, another problem arises in that the manufacturing cost of the optical subassembly 2700 becomes high.